Cooperative Self-Assembly Driven by Multiple Noncovalent Interactions: Investigating Molecular Origin and Reassessing...

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Solid-State NMR Spectroscopy

Background:

• Cooperative interactions are crucial for programmable supramolecular assembly but are often based on empirical knowledge.
• Rational design of molecular self-assembly requires detailed characterization of underlying interactions, especially in disordered aggregates.
• Understanding these interactions is key to controlling material properties and functions.

Purpose of the Study:

• To elucidate the key structure-directing interactions in cooperatively bound perylene bisimide (PBI) aggregates using advanced solid-state NMR techniques.
• To investigate the synergistic effects of π-stacking and hydrogen bonding on cooperativity in PBI assemblies.
• To explain the anomalous solvent-induced disassembly of these aggregates and compare it with thermal disassembly.

Main Methods:

• Extensive one- and two-dimensional magic-angle-spinning (MAS) solid-state NMR spectroscopy.
• ¹H-¹³C cross-polarization heteronuclear correlation (CP-HETCOR) and ¹H-¹H double-quantum single-quantum (DQ-SQ) correlation spectroscopy.
• Optical absorption, circular dichroism, and NMR titration experiments.

Main Results:

• Identification of specific through-space ¹H···¹³C and ¹H···¹H proximities, revealing molecular organization in solid PBI aggregates.
• Elucidation of cooperativity arising from the synergy between strong π-stacking and weaker interstack hydrogen bonding.
• Observation and explanation of anomalous solvent-induced disassembly, highlighting differences between solvent and thermal disassembly pathways.

Conclusions:

• Solid-state NMR is a powerful tool for characterizing interactions in disordered supramolecular assemblies.
• Cooperativity in PBI aggregates is driven by a combination of π-stacking and hydrogen bonding interactions.
• The study reveals distinct mechanisms for solvent-induced versus thermal disassembly, offering insights for controlling supramolecular structures.